I’ve always fancied trying seitan but you have to go all the way to Holland and Barrett to get the vital wheat gluten and then physically make the stuff yourself. That’s almost as much work as actually physically killing an animal myself. No thank you, if you want me to be ethical then please do all the work for me Mr Tesco
I've seen seitan in strange places, including Asda, healthfood/wholefood stores, and Chinese supermarkets. It's sometimes available in tins, sometimes frozen, sometimes in chillers, sometimes marketed as fake duck (although not all fake duck is seitan), although it's still not very common. It is texturally different to most meat substitutes, but again doesn't actually taste of anything (although it seems commonly sold with flavouring).
Deep fried tofu puffs are also good, if you stumble upon any (fluffy and light with lots of holes, totally different texturally to regular tofu, and tasting of grease) - also related is amuraage, Japanese fried tofu skins, which are again like slightly bland grease, but you could say the same about chips. All can be stuffed or put in soups.
re jackfruit: it's nice in pulled jackfruit which you make by cooking it in barbecue sauce with onions for about an hour, but it has a weird mouthfeel in curries, a bit like artichoke hearts but not as nice.
Mentioning terrible vegan substitutes, vegan feta is hilariously bad, more like cubes of coconut flesh than anything cheesy. Vegan cheese is really not as good as vegan meat.